1. Field of the Invention
The present invention relates to a device, hereinafter abbreviated DME, and a process for distributing, mixing, adding, and/or removing several fluids, at least one main fluid and at least two other secondary fluids.
The invention is applied in particular in the field of chromatography for fluids in the gaseous, liquid, or supercritical state.
2. Description of the Prior Art
When separation processes by distillation are ineffective, it is possible and normal to call on simulated fluidized-bed systems to separate substances containing for example several different chemical compounds or substances containing isomers.
Chromatography processes generally use several fluids, called secondary fluids to distinguish them from the main fluid or substance to be separated, circulating in the chromatography column.
These secondary fluids can be of different kinds and can be removed from the column or injected into the column for example at the DME.
This difference in the nature of the fluids leads, for example, to risks of contamination, as one fluid may be in contact with another fluid, requiring additional flushing operations when a common injection a removal circuit is used for the various secondary fluids.
In addition, during chromatography, particularly at the end of the removal operation of a first fluid, a plug or remnant of this fluid is left behind, which needs to be eliminated before a second fluid is removed and/or injected.
For this purpose, a preliminary operation consists of pushing out or removing this plug from the column.
The flushing operations normally conducted to clean and/or drain the circuits contribute to increasing the complexity of the stages of the process used in the column as well as its cost and can decrease its efficiency.
Moreover, in certain processes, it is very important to achieve distribution or collection of the fluids circulating in the bed that is as homogeneous as possible.
In particular, in the area of simulated fluidized-bed chromatography, usually operated in a simulated countercurrent, and which in the majority of cases combines columns with large diameters or sections, and numerous separation stages, it is thus necessary to have one DME between each separation stage to ensure that the main fluid (A) is collected as uniformly as possible and that one or more secondary fluids are distributed and/or removed, and that the mixture formed inside the DME is redistributed.
Hence it is very important to render propagation of the main fluid in the column as uniform as possible by having a piston-type flow. One of the means of achieving this is to minimize the differences in travel time between the various flow lines of the flowing fluid, or between the various fluid particles, before they enter the mixing chamber. This is because these flow lines will have different path lengths and travel times depending on the position of their circulation route inside the column, this route being for example referenced with respect to the column axis (or to one of its walls), and to the position of the mixing chamber, particularly the opening of the chamber allowing fluid to pass.
For example, when the mixing chamber is disposed substantially in the center of the column and at an opening located in the vicinity of the central axis of this column, the travel time for a line of fluid circulating near the outer wall of the enclosure is greater than the travel time of a line of fluid circulating near the center of the column.
These differences in travel time bring about displacements in the arrivals of the flow lines or fluid lines in the mixing chamber which can bring about perturbations in the level of the traveling front of the main fluid. This lack of homogeneity in arrival times may affect the mixing quality in this chamber and perturb the various main fluid propagation streams advancing or propagating "piston-wise."
Among the distributor systems or DMEs described in prior publications and used industrially for specialty chemicals, laboratories, or large industries, the Amicon Company offers a DME that has a central baffle-distributor system that leads to correct distribution of the main fluid with small dead volumes. However, it does not have means of adding and/or removing a secondary fluid, nor means for optimally mixing a main fluid with a secondary fluid.
Moreover, the central baffle system brings about some perturbation in radial distribution of the main fluid, and the pressure drop is relatively great due to high flowrates at the relatively small central collecting point in the distributor.
It will be remembered that the terms "upstream" and "downstream" are relative to the circulation direction of the main fluid circulating in the beds of granular solids and passing through the DME.
U.S. Pat. No. 3,948,775 describes a DME used in a chromatography column with two beds in which the main fluid (A) is collected downstream from a grid located at the outlet of the first bed by a conduit and sent to a point upstream of the second bed, and from a collecting grid by a conduit, before being redistributed laterally in the second bed. The secondary fluid (B) can be introduced via an additional conduit and mixed in line with the main fluid, with the mixing taking place essentially at one point. The collecting and redistribution areas are separated by an inclined fluidtight baffle and thus allow conical collection with a small dead volume.
Nonetheless, the existence of an outside line creates an additional dead volume that can generate a back-mixing phenomenon and additional pressure drops.
Moreover, because of its lack of symmetry, the lateral distribution of the fluids can bring about imperfect homogenization for columns that have large diameters.
The teaching contained in U.S. Pat. No. 3,214,247 consists of collecting all the main fluid downstream of a baffle and then channeling it into a space delimited by the baffle and injection means for a secondary fluid. The main fluid channel is mixed in the space thus defined with the secondary fluid distributed in the form of transverse jets, and the resulting mixture is then redistributed in the space located below the baffle before being sent to the second bed. Because of the inclined shape of the baffle walls, this device has small dead volumes and the pressure drop created is relatively moderate because of the transverse collection.
However, the main fluid collecting space, the secondary fluid injection space, and the mixing space are not precisely delimited, which prevents the mixing function from being totally controlled. Moreover, as the mixing area is not confined to the central area, back-mixing phenomena may then occur throughout the conical collecting and/or redistribution section.
U.S. Pat. No. 3,723,072 describes a device for mixing two fluids inside a mixing chamber before redistributing the mixture in a secondary bed. This device provides a mixture redistribution means that does not optimize redistribution in the bed and does not avoid the perturbation induced because the differences in propagation time of the main fluid lines in the upper bed vary in their position relative to the enclosure and the entry point into the chamber.
However, none of these devices describes or suggests using several injection and/or removal circuits "dedicated" to one fluid, namely used for passage of a predetermined fluid, thus overcoming the above-mentioned drawbacks.
The word "dedicated" in the context of the invention means that an injection and/or removal circuit sees only the passage of a predetermined fluid when the process is implemented.